The invention relates to a blade ring for air-swept roller mills having an outer ring and an inner ring, between which are positioned guide blades, accompanied by the formation of flow ducts.
Air-swept roller mills, bowl mills or also vertical air flow mills have grinding rolls rotatable about a fixed axis and which are placed on a rotary grinding bowl. Between the grinding bowl and the mill casing is formed an annular space, in which are positioned substantially radially oriented guide blades for guiding an upward carrier gas flow, e.g. an air flow, with which the ground material is supplied to a classifier. The annular space is constructed as an annulus and with the guide blades located therein is referred to as a blade ring and sometimes as a nozzle ring.
Known blade rings comprise a rolled, cylindrical or conical outer ring and inner ring or a combination of a conical outer or inner ring and a cylindrical inner or outer ring, between which are positioned the guide blades. The guide blades form flow ducts, which generally have a rectangular cross-section.
Apart from these blade rings comprising rolled rings and welded in guide blades, cast blade rings are also known.
Relatively high manufacturing costs are involved in the case of the known blade rings. Particularly with large roller mills, which can have blade rings with an external diameter up to 7 m, manufacture is extremely costly. The one-piece, annular blade rings are also difficult to transport and install and are consequently supplied in segmented form or as annular sectors to the building sites and are assembled there. However, segmentation presupposes an annealing treatment, so that the ring structure is stress-relieved and the separating cuts for producing the segments give rise to no deformation, particularly cracking.